Electric screen device

ABSTRACT

An electric screen device for preventing creatures from intruding into a water channel, which comprises a pair of opposed electrode assemblies disposed on opposite sides of a water intake channel, and a dc pulse applying device  13  for applying dc pulses between the electrode assemblies. In such electric screen device, the product of the peak value of the intensity of an electric field produced between the electrode assemblies by the dc pulse applying device and the body length of creatures to be prevented from intrusion into the water channel is not less than 0.1 V, the dc pulse applying time is within the range of 2-200 msec, and the duty factor of the dc pulse is not more than 0.5.

TECHNICAL FIELD

The present invention relates to an electric screen device forpreventing creatures, such as fishes and shellfishes, from intrudinginto a water intake port, i.e., a water intake channel or the like in apower plant or the like.

BACKGROUND ART

To prevent creatures, such as fishes and shellfishes, from intrudinginto a water intake port in a power plant, a water intake channel isprovided with an electric screen device.

Conventionally, this electric screen device comprises a pair of opposedelectrode assemblies disposed on opposite side walls of the water intakechannel, and a voltage applying device for applying dc or ac voltagebetween said electrode assemblies at predetermined intervals of time.

Thus, an electric screen is formed by a predetermined voltage appliedbetween said electrode assemblies at predetermined intervals of time bythe voltage applying device.

The applied voltage is of a value such that the product of the peakvalue of the intensity of an electric field and the voltage applyingtime (on-time) is not less than 0.01 V sec/cm, and the off-time is setwithin the range of 0.5-3 sec. Empirically, it has been so set for thecase of sweetfish of 10 cm length that the peak value of the electricfield intensity is 0.08 V/cm and the on-time and off-time arerespectively 2 sec.

According to the electric screen device described above, however, theoff-time is relatively long, which fact is preferable from the viewpointof power saving but poses a problem that it permits intrusion ofcreatures.

Accordingly, it is an object of the invention to provide an electricscreen device which is designed to save power and to reliably preventintrusion of creatures.

DISCLOSURE OF INVENTION

An electric screen device according to the present invention comprises apair of opposed electrode assemblies disposed on opposite sides of awater channel, and a dc pulse applying device for applying dc pulsevoltage between said electrode assemblies to prevent creatures fromintruding into the water channel, said electric screen device beingcharacterized in that the product of the peak value of the fieldintensity (voltage per unit of length) of an electric field producedbetween said electrode assemblies by said dc pulse applying device andthe body length (unit of length) of creatures to be prevented fromintrusion into the water channel is not less than 0.1 V and in that thedc pulse applying time is within 2-200 msec. Further, in the abovearrangement, the duty factor of the dc pulses is not more than 0.5.

According to the above arrangement, since the product of the peak valueof the intensity of the electric field produced between the electrodeassemblies disposed on opposite sides of the water channel and the bodylength of creatures to be prevented from intrusion is not less than 0.1V, and since the dc pulse applying time is within the range of 2-200msec, intrusion of the creatures can be efficiently prevented.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view of a water intake channel provided with apreferable electric screen device according to the present invention;

FIG. 2 is a plan view of the water intake channel provided with saidelectric screen device;

FIG. 3 is a waveform diagram of dc pulses to be applied by said electricscreen device;

FIG. 4 is a graph showing the relationship between the peak value of theintensity of an electric field, which value indicates the paralysislimit of creatures, and the body length of creatures to be preventedfrom intrusion; and

FIG. 5 is a graph showing the relationship between the peak value of theintensity of the electric field, at which value creatures showabhorrence, and the on-time.

BEST MODE FOR EMBODYING THE INVENTION

The invention will now be described in more detail with reference to theaccompanying drawings.

FIG. 1 is a sectional view of a water intake channel provided with anelectric screen device, and FIG. 2 is a plan view thereof.

As shown in FIGS. 1 and 2, the numeral 1 denotes a water intake channelleading to a port for taking in cooling water, e.g., in a power plant,with an electric screen device 2 installed somewhere between the ends ofsaid channel.

This electric screen device 2 comprises a pair of electrode assemblies12, 12 disposed on opposite side walls la of the water intake channel 1,each assembly being composed of a plurality of electrode rods 11disposed at predetermined intervals, and a dc pulse applying device 13for applying dc pulses between said electrode assemblies 12, 12 under apredetermined voltage and at predetermined intervals of time. Further,the electrode rods 11 are vertically installed.

And dc pulses as shown in FIG. 3 are applied to said dc pulse applyingdevice 13. The application of these dc pulses is such that the productof the peak value F of the intensity of an electric field producedbetween said electrode assemblies 12, 12 and the body length L ofcreatures to be prevented from intrusion into the water intake channel 1is not less than 0.1 V, and that the on-time (the dc pulse applyingtime) is within 2-200 msec. In other words, the product of the peakintensity and the body length can be expressed in terms of units asV/cm×cm=V, and according to the invention the magnitude of the intensityand of the length of the creatures is not less than 0.1 V. In FIG. 3, t₁is the on-time and t₂ is the off-time.

Based on the curve found by investigating the electric shock region forcreatures shown in FIG. 4 (the region being shaded), it is determinedthat the product of the peak value E of the intensity of the electricfield and the body length L of the creatures should be in the range ofnot less than 0.1 V.

Further, it is determined that the on-time for dc pulses should bewithin the range of 2-200 msec on the basis of the results of aninvestigation of the limit at which the creatures (e.g., sweetfish,crucian carps, carps, etc.) show abhorrence of electric stimulus, asshown in FIG. 5.

FIG. 5 shows that in the case where the body length of creatures such asfish is 10 cm and the duty factor expressed by on-time divided by(on-time+off-time) is 0.2, the proper range of the on-time t₁, in whichthe creatures show their abhorrence is 2-200 msec.

Stated in more detail, if the on-time t₁ is shorter than 2 msec, thepeak value of the electric field intensity is required to be higher thanthat when the dc source is used, thus, this is disadvantageous. Further,if the on-time t₁, is longer than 200 msec, there arises no differencefrom the case where the dc source is used, which means that the effectsof pulses are lost. That is, the result is a discontinuous electricscreen rather than in the form of pulses, permitting creatures tointrude. Therefore, the limit of the on-time t₁ should be 200 msec.

The above description has been given with reference to the case wherethe duty factor is 0.2. In the case where the interval between adjacentpulses is longer, a value greater than 0.5 may be employed, though 0.5or less is preferable.

Further, in the above embodiment, the electric screen device has beendescribed with reference to the case where it is installed in a waterintake channel in a power plant. However, it may be installed in a waterdischarge channel. Further, it may be installed in either water intakechannel or water discharge channel in a water control system.

According to such electric screen device, since the product of the peakvalue of the intensity of the electric field produced between the pairof electrode assemblies disposed on opposite sides of the water channeland the body length of creatures to be prevented from intrusion is notless than 0.1 V, and since the dc pulse applying time is within therange of 2-200 msec, the power consumption is less than the case of aconventional device and intrusion of creatures can be efficientlyprevented.

INDUSTRIAL APPLICABILITY

As described above, the electric screen device of the invention isinstalled in the water intake channel leading to the water intake portin a power plant, so that fishes and shellfishes can be reliablyprevented from intruding into the water intake channel, thus being veryuseful.

What is claimed is:
 1. An electric screen device for preventingcreatures from intruding into a water channel, comprising a pair ofopposed electrode assemblies disposed on opposite sides of the waterchannel, and a dc pulse applying device for applying dc pulses betweensaid electrode assemblies, characterized in that: the product of thepeak value of the intensity of an electric field produced between theelectrode assemblies by said dc pulse applying device and the bodylength of creatures to be prevented from intrusion into the waterchannel is not less than 0.1 V, and the dc pulse applying time is withinthe range of 2-200 msec.
 2. An electric screen device as set forth inclaim 1, wherein the duty factor of each dc pulse is not more than 0.5.